As for the traditional telecommunication switch equipments, the switch control was mainly hardware-based. Under such condition, the control domain of each equipment was fixed, and the controlling devices and the controlled equipments were connected by electrical cables. Therefore, it was nearly impossible for such system to realize disaster recovery with controlling devices in different places.
The next generation network employs soft-switch as core control, and employs packet switch network as transmission network instead of the fixed electrical cable connection, and making it possible to provide a control device with disaster recovery function. But the current core control devices in next generation network have not provided disaster recovery function yet.